Various industries in the world use large furnaces to melt and hold their product. Example industries are the glass industry and the steel industry. These furnaces may be as large as small buildings. They are constructed using refractory material with very high melting temperatures and good insulation properties (to contain the heat). During operation of these furnaces, the refractory walls of the furnace will degrade. This degradation takes the form of inner surface erosion, stress cracks, and material incursion into the molten material. At this time, there is no well established method of deterministically measuring the thickness of the walls of such furnaces. Because of this, members of the industry must shut down and replace the furnace walls based on estimates of the expected lifetimes of the furnaces. This is an expensive process, and wasteful if done too soon, but dangerous to human life if delayed for too long. The flow of molten glass at such high temperatures inevitably leads to erosion and degradation in the refractory lining and creates a high risk for molten glass leakage through the wall. Once the molten glass leaks through the gaps and cracks in the furnace walls, it causes significant damage to the capital equipment around the furnace and, most importantly, causes significant production disruption. A major leak may require at least 30 days of production disruption before the furnace can be restored to operating mode because it needs to be cooled down, repaired and fired up again.
Another issue is that the refractory material used to build the furnace walls may have defects not visible by surface inspection. The customer purchasing this material would like to have a means for performing internal inspections during the acceptance process from the manufacturer, or the manufacturer would like to have a means for performing internal inspections during manufacture (either to optimize the process, perhaps in real time, or to classify material to be delivered as “without flaws”).
Previous efforts have been made to utilize microwaves to detect thickness of materials such as furnace walls, as described for instance in U.S. Pat. No. 6,198,293 to Woskov et al., the specification of which is incorporated herein by reference. However, such prior efforts have met with difficulty. More particularly, while efforts have been made to attempt to determine furnace wall thickness on hot furnaces, those efforts have been generally unsuccessful (it having been discovered by the inventors herein that particularly low frequency bands should be used so as to reduce signal loss and to be able to successfully evaluate the interior condition of such surfaces). Moreover, in placing system components close to the surface to be evaluated, spurious signal reflections have made it quite difficult to isolate what is truly the reflected signal that is of interest, thus further complicating the effort of evaluating the interior condition of such surfaces.
Thus, there remains a need in the art for systems and methods capable of remotely evaluating the condition of such surfaces, such as through reflected microwave measurements, that avoid the problems of such prior art systems.